There are, in general, two kinds of whey that are produced as by-products during processing of milk in the manufacture of dairy products such as cheese and curd. These are commonly referred to as sweet whey and sour whey.
Sweet whey is also termed cheese whey and is produced during cheese making, when rennet (an enzyme derived from a calf's stomach) is used for curdling. The pH value of sweet whey can range between 5.2 and 6.7.
Sour whey comprises the whey type commonly known as acid whey and curd or cottage-cheese whey. Acid whey, also known as casein whey, originates from the manufacture of casein by means of lactic acid, lactic acid generating bacteria or hydrochloric acid. As suggested by their names, curd or cottage-cheese whey are produced during the manufacture of quark and cottage-cheese. Lactic acid generated by natural fermentation imparts a high acidity to the whey such that the pH values of these types of whey typically range from 3.8 to 4.6.
In some cases, sour sweet whey is also considered encompassed by this term although this may appear incorrect. If insufficient care is given to sweet whey (cheese whey) it becomes sour by continued natural fermentation and is then referred to as sour sweet whey. This additional fermentation process is usually not desired.
Typical compositions of these types of whey are shown in the following table:
SWEETSOURWHEYWHEYSolids (% by weight)6.4-6.86.8Lactose (% by weight)4.84.3-4.4Protein (% by weight)0.750.8Fat (% by weight)0.05<0.01Ash (% by weight)0.60.80pH6.14.6Reference: Zadow, J. G.: Whey and lactose processing, Elsevier Applied Science, 1992
If the whey is treated by means of ultrafiltration to recover valuable proteins, the product stream with lower protein content is the so-called whey permeate. Whey permeate is therefore also a by-product of cheese manufacture which accrues during protein recovery from whey by means of ultrafiltration.
Its use in downstream dairy processes and food production is limited due to the high mineral content and the poor sweetness. Therefore, so far whey permeate is brought to the market as a very low value product, being used in fertilizer and animal feed.
Applications of whey permeate creating more value are desirable. This could be accomplished by providing a method to transform whey permeate into a raw material for “dry applications” such as confectionery, biscuits, powdered soft drinks and other categories.
In the past, sweet whey powder (SWP) has been employed as a low-price substitute for sucrose in confectioneries and, in particular, in chocolate. However, any further increase of the SWP content and, thus, a further reduction of the costs of the ingredients is limited by                the mineral content which leads to undesirable off-flavours,        the high content of α-lactose which is the crystalline form of lactose usually resulting from spray-drying and which causes a powdery mouthfeel and lack of sweetness, both of which is undesirable in chocolate products, and, independently,        the whey proteins present in SWP are not available for other economically more beneficial applications such as valuable nutrition products although they appear to have no functionality in chocolate products.        
In particular in view of the latter issue, it is desirable to replace the SWP in chocolate products by another raw material that is available at lower costs, for instance, a powdery raw material derived from whey, in particular, whey permeate.
It is essential that such a raw material for dry applications has immaculate flavour properties and processability, i.e. no salty or metallic off-flavour and a low tendency of caking. The latter is important not only for later applications but also during manufacture, for instance, by spray-drying. Advantageous caking properties can be achieved if the formation of amorphous forms of lactose during drying is avoided. Furthermore, whey permeates originating from cottage cheese and casein production is known to be difficult to dry due to its high content of lactic acid. It tends to agglomerate and form lumps upon spray-drying. Independently, a method has to be found to lower the mineral content of whey permeate.
Removal of minerals in whey and whey permeate has, for instance, been addressed in the following prior art documents:
Zadow (in “Whey and Lactose Processing”, Elsevier 1992, pages 83-85) discloses the processes of ion-exchange, lactose crystallization and spray-drying and shows some linkage between them. The reference mentions the influence of crystallization on the hygroscopicity of the product and, hence, on the processability during spray-drying, but the reference does not teach that this step is not sufficient to achieve good processability, but a previous demineralization step is necessary.
WO 02/50089 discloses a method for purification of lactose in a whey product using two demineralization steps and an additional crystallization step. The second demineralization step includes the addition of alcohol in order to precipitate minerals. This reference is related to the production of edible high-purity lactose (99.8%). Treating the whey with ion-exchange resin(s) is mentioned as a method suitable for the first demineralization step in order to remove divalent ions, although disadvantages of an ion-exchange step are discussed.
US Patent Publication 2003/0000894 discloses a process for treating liquids, such as a citric acid fermentation broth, including a nanofiltration step and an ion-exchange step.
U.S. Pat. No. 6,475,390 and EP-A-01541032, both emanating from PCT/AU98/00588, disclose a process for purifying biological molecules, such as lactose, from dairy streams, such as sweet cheese whey permeate or acid whey permeate, which combines two demineralization steps. A cation exchanger is used to remove the divalent cations in the first step and nanofiltration is used to remove monovalent ions in the second step. The permeate of the nanofiltration step is used to regenerate the ion exchanger resins.
EP-A-0083325 discloses a process for the manufacture of a sweetener, in which lactose is dissolved in water and subsequently hydrolyzed to glucose and galactose by means of a strongly acidic cation exchanger.
U.S. Pat. No. 4,971,701, U.S. Pat. No. 6,033,700, EP-A-0315135, and EP-A-0835610 disclose processes for removing at least a portion of salts contained in whey by means of electro-deionization using ion-exchange membranes. U.S. Pat. No. 6,033,700 and EP-A-0835610 mention that demineralized milk and milk derivatives may be useful for replacing skimmed milk in the manufacture of confectionery-chocolate. Acid whey and sweet whey obtained from an ultrafiltration step are mentioned as starting materials for the disclosed deionization process. However, neither of these prior art references contain any teaching regarding the organoleptic properties of the obtained demineralized whey products and their suitability in confectionery such as chocolate and other products. Thus, there still remains a need for solutions to the problems outlined hereinabove, viz. to provide a process for producing whey powder from whey permeate suitable to be used in biscuits, powdered soft drinks, and confectionery products, including chocolate products.